SiC single crystals are thermally and chemically extremely stable, are superior in mechanical strength, and resistant to radiation, in addition, have superior properties such as high breakdown voltage and high thermal conductivity in comparison to Si (silicon) single crystals, enable enable p- and n-conductivity electronic control by adding impurities, and have wide forbidden bandwidths (approximately 3.3 eV for 4H-type single crystal SiC, approximately 3.0 eV for 6H type single crystal SiC). Therefore, realization of high temperature, high frequency, voltage resistance/environment resistance which could not be realized with Si single crystals, GaAs (gallium arsenide) single crystals, and other existing semiconductor materials is possible. Expectations of these as next generation semiconductor materials are rising.
Conventionally, the gas phase method and the solution method are known as typical growth methods of SiC single crystals. As the gas phase method, normally the sublimation method is used. The sublimation method comprises arranging SiC material powder and an SiC single crystal seed crystal facing each other in a graphite crucible and heating the crucible in an inert gas atmosphere to epitaxially grow the single crystal. However, it is known that with this gas phase method, the polycrystals growing from the crucible inner walls negatively affect the quality of the SiC single crystal. Further, the solution method comprises using an SiC single crystal production system which has a basic structure comprised of a crucible for holding a starting solution, a starting solution, a high frequency coil or other external heating system, an insulator material, a seed crystal support member that can be lowered and raised (for example, a graphite rod), and a seed crystal attached at the tip of the seed crystal support member, dissolving C (carbon) from a C supply source, for example, a graphite crucible, into an Si melt, an Si alloy melt in which metal had been dissolved, or another Si-containing melt in the crucible to obtain a starting solution, and growing an SiC single crystal layer on the SiC seed crystal through solution precipitation.
In such a method of growing an SiC single crystal by the solution method, use is made of either the SiC single crystal growth method of the method of growth by providing a temperature gradient to the starting solution so that the solution temperature around the seed crystal becomes lower than the solution temperature at other parts or the method of growth by slowly cooling the entire starting solution.
For example, Japanese Patent Publication No. 2007-186374A describes a method of production of an SiC single crystal which maintains a temperature gradient inside a Si melt in a graphite crucible where the temperature falls from the inside toward the melt surface while growing the SiC single crystal wherein the method applies to the melt in the crucible a vertical magnetic field directed upward from the bottom of the crucible to the melt surface. As a specific example, it shows that by applying a vertical magnetic field directed upward toward the melt surface, it is possible to suppress the natural convection in the Si melt and thereby raise the transport efficiency of C (carbon) from the bottom of the crucible to the seed crystal and raise the speed of growth of the SiC single crystal to about 160 μm/hour.
Further, Japanese Patent Publication No. 2007-223814A discloses a method of production of a single crystal semiconductor which brings a seed crystal to which an impurity has been added into contact with a melt in a crucible and pulls up the seed crystal to thereby produce a single crystal semiconductor, which method of production of a single crystal semiconductor includes a step of applying a magnetic field to the melt, a step of making the seed crystal contact the melt, and a step of pulling up a single crystal semiconductor without necking after the seed crystal contacts the melt. As a specific example, it shows the example of applying a magnetic field to the melt 40 minutes or more before making the seed crystal contact the melt and continuing application of the magnetic field until the silicon single crystal finishes being grown so as to obtain a single crystal silicon semiconductor.
Japanese Patent Publication No. 2009-091233A describes a silicon ingot growth method which includes a step of heating a quartz crucible in which silicon has been charged and applying a 500 Gauss or more magnetic field to the inside of the quartz crucible while making the silicon melt and a step of applying a less than 500 Gauss magnetic field to the inside of the quartz crucible while growing a single crystal silicon ingot from the melted silicon.
Japanese Patent Publication No. 2009-274887A describes a method of growing an SiC single crystal on an SiC seed crystal from an Si—Cr—C solution comprised of a Si—Cr melt into which C has been dissolved wherein the method of production of a single crystal applies a DC magnetic field to the Si—Cr—C solution. As a specific example, it shows an example of using an SiC single crystal growth system which arranges a magnetic field coil at the outside of a high frequency heating coil so as to grow an SiC single crystal under conditions of a growth time of 10 to 20 hours or so and application of a magnetic field whereby a 270 μm/hour or so speed of growth of SiC single crystal is achieved and shows that the direction of the magnetic field is not limited.
Japanese Patent Publication No. 2012-193055A describes a method of production of an SiC single crystal which uses a solution method SiC single crystal production system wherein the method of production of an SiC single crystal uses as at least part of the support part a thermal conducting anisotropic support part which is comprised of a member which has a relationship TCH>TCV between a thermal conductivity (TCV) in a direction supporting the crucible and a thermal conductivity (TCH) in a direction vertical to that direction and uses high frequency heating to heat the solution to suppress the formation of polycrystals.